Injection molding apparatuses, such as hot halves and hot runners, commonly use valve pins to control flow of molding material.
Improper valve pin operation can cause damage to a valve pin itself or to surrounding components, such as a nozzle tip, nozzle tip liner, nozzle tip guide sleeve, or mold gate. For example, on the close stroke, when the tip of a valve pin is pushed into the mold gate area, the tip of the valve pin can collide with a foreign object blocking the mold gate. Such a foreign object may be a contaminant. Unexpectedly frozen molding material in the gate area can also act as a blockage. The result is that damage to the valve pin or surrounding components can occur. Similarly, a valve pin can seize before reaching the end of its close stroke, whether this be induced by material seeping between surfaces having a high-tolerance sliding relationship or by some other cause. These problems can be exasperated when several valve pins are ganged together to be actuated in unison by, for example, a common valve pin plate. In this case, the entire force transmitted by the actuators to all the valve pins may be taken by a single valve pin that encounters a blockage, becomes seized, or encounters some other motion inhibiting condition.
Replacement of a damaged valve pin or related component can be time consuming and costly.